Just want to echo what others have said -- I think we overblow the importance of caliber, when what really matters is having a firearm, the proper training, and a defensive mindset. In the overwhelming majority of cases, simply having (and being prepared to use) a firearm will deter an attack. Consider:
Dr. Gary Keck's (pro-CCW) research showed that less than 47% actually pointed their firearms at the criminal, less than a quarter (22%) actually fired, less than 15% fired intending to hit someone (the other 7% were warning shots), and less than 8% actually hit their targets. In other words, your odds are less than 1/10 that "caliber" will actually be a factor in a defensive engagement. The other 90% of the game, so to speak, is having a firearm, proper training, and a defensive mindset.
But that's even assuming you get into a gunfight. If we step back further...according to the FBI,
there were 1,318,398 violent crimes in 2009 (out of 307,006,550 Americans). Let's assume for a moment that every single one of those victims had a firearm (if only that were true). Taking into account Dr. Keck's research and making some statistical assumptions (8% of 1,318,398 of 307,006,550), you come to the rough analysis/conclusion that in 2009, caliber "mattered" (or would have mattered) for only 0.0343% of all Americans. Of course, this isn't even taking demographics into account. Are you male or female? How old are you? Are you a member of a minority group? What is your socioeconomic status? Do you live in an urban, suburban, or rural area?
Your chances of encountering violent crime dramatically increases (or drops) depending on who you are, where you live and what you do.
Compare that to auto accidents --
6,420,000 auto accidents in 2005, in which 2,900,000 Americans were injured and another 42,636 killed.
Can we agree that it's far, far, far more likely that the average CCW permit-holder will get into a serious car accident tonight than will engage in a gun fight with a gaggle of 6'5" drugged up crazies? Well then why don't we get into "caliber wars" about our vehicles -- comparing crash test ratings and consumer reports and the efficacy of this car's safety features over the merits of that one in some sort of hypothetical worst-case scenario accident?
Do you see what I mean? In the long run, the caliber wars are a bit silly since they matter (on average in any given calendar year) for only 0.03% of us. Don't get me wrong -- most of us are firearms enthusiasts on a firearms forum, so it's fun to debate this or that, but I think most of us would also agree that all handgun calibers suck. Some just suck less. What we should focus on is having a firearm, the proper training, and a defensive mindset.
(Thankfully, most thoughtful/wise/experienced forum users repeat this mantra to new TFLers who post "HI! I just got my CCW. SO EXCITED! I am looking for the perfect gun in the perfect caliber. What should I get? Also, is it true that there is a place in a man's head that, if you shoot it, it will blow up?")